17. v PREP n △You use at to show that someone is doing something repeatedly.
6. used after a verb △to show that someone tries to do something, or partly does something, but does not succeed or complete it.
- She lowered the handkerchief which she had kept dabbing at her eyes...
- Miss Melville took a cookie and nibbled at it.
- He clutched wildly at the rope as he fell.
- She nibbled at a sandwich (= ate only small bits of it).
8. used to show △the situation someone or something is in, what someone is doing, or what is happening
- I am afraid we are not at liberty to disclose that information...
- Their countries had been at war for nearly six weeks.
- The country is now at war.
- I felt like I was at a disadvantage.
- I think Mr. Harris is at lunch.
...... COBUILD, OALD
16 [PREP] △You use at to say how something is being done.
- Three people were killed by shots fired at random from a minibus...
- Mr Martin was taken out of his car at gunpoint.
- Eleanor was annoyed at having had to wait so long for him...
- The British team did not disguise their delight at their success...
* * *
- It is not possible to make profits by acting on old information or at patterns of past price changes.
Let's try to catch different images between:
- act on old information
- act at patterns of past price changes